Because clogged gutters and downspouts can cause rainwater backup and damage to buildings and defeat the intended purpose of safe diversion of the water, protective screens have been used.
Typically, these are of hardware cloth (sometimes called "rat wire") with quarter-inch to half-inch (6 mm to 12 mm) mesh heavy enough to support a mass of wet leaves. On seeing such accumulation, the homeowner or other person responsible must climb up and remove the debris, at some risk of falling and with some loss of time.
Coarseness of the mesh permits stems and fragments to penetrate it and hang, and in part to drop through into the gutters when clearing is attempted, making the screen and gutters difficult to clean. Further, the gutters must sustain a load of debris and water and heavy mesh for which they are not intended. In mild weather insects such as mosquitos may breed in the gutters in pools formed by incomplete drainage.
Should the heavy hardware cloth blow loose, it can cause injury and short-circuit electric lines. Being usually of galvanized steel, it can cause electrolytic reaction with aluminum gutters.